Continuous process for manufacture of perchloromethyl mercaptan



Dogd E. Hudson Jr.

b5 Gbbor'ne Patented Nov. 13, 1951 Ernest 0. Ohsol, Cranford, Carl S.. Carlson, Roselle. and Boyd E. lHudson, Jr., Cranford, N.- Je., asslgnors to Standard Oil Development Company,'a corporation of Delaware Application August 4, 1949, Serial No. 108,584

3 Claims, (Cl. Mil-543) This invention relates to an improved process .for the preparation of perchloromethyl mercaptan.

' Perchloromethyl mercaptan is an important intermediary in the manufacture of lube 'j oil liquid materials encountered in the process of additives and parasiticides. It'is conventionally l prepared in a batch process employing stoichiometric amounts of carbon disulfide and chlorine This process suffers from several disadvantages. The boiling point of SzClz is 137 C., which is close to that of perchloromethyl mercaptan which boils in the range of 142l49 C. and hence it is usuallyv necessary to separate the two by steam distillation. Steam hydrolyzes SzClz in the manner shown in Equation'2:v

The products of Equation 2 are highly corrosive and contain, in addition, iinely-divided sulfur,l making it a very diflicult mixture to handle on alarge scale basis. Some of the-sulfur liberated is in the vapor phase which results in clogging and fouling of equipment.

In addition, during the course of the reaction. some carbon disulfide reacts as indicated in Equation 3:

This results in an undesirable production of carbon tetrachloride and a reduction in the selectivity in the direction of the production of the perchloromethyl mercaptan. This reaction, of course, also produces additional SzClz, from which the perchloromethyl mercaptan has to be separated.

The present invention provides a method for obtaining perchloromethyl mercaptan relatively free of S2012. The improved method comprises conducting the reaction in a continuous manner sothat formation of SCI: rather thanSzClz is favored, and also rapidly removing the lizlClz and other reactive materials from the perchloromethyl mercaptan under relatively non-re active conditions so that undesirable degradation and reduction in yields of the perchloromethyl mercaptan are avoided.

SClz boils at a temperature of 59 C. and in the process of this invention wherein its reactivity is minimized, it can be readily separated from perchloromethyl mercaptan which boils at a temperature of at least 83 C. higher. For

this invention are listed below in Table I:

Table I Boiling points CS2 i 6"C. sch j. .--ssf c. CC14 77 C. S2Cl2 ..-137 C. Perchloromethyl mercaptan 142149 C.

At low temperatures, i. e., below 25 C., and preferably temperatures in the range of 0l5 C., the reaction proceeds according to the process of this invention inthe manner indicated in Equation 4:

: SClz is a powerful chlorinating agent, however. as indicated by Equation 5:

The mechanism of Equation 5 is capable of reducing the selectivity to perchloromethyl mer- `captan by the undesirable reaction of Equation 3above. The maintenance of the reaction zone within the temperature range of this invention prevents to a substantial extent these latter two reactions (Equations 5 and 3).

Another difliculty overcome in the process of this invention is the reaction indicated in Equation 6:

The reaction of Equation 6 would also diminish the yields of desired production.

Thus the undesirable side and degradation reactions which prevent the reaction from proceeding in the manner indicated by Equation 4 are greatly diminished by cooling the exothermic reaction to the temperature range indicated. In addition, according to the process of this invention the perchloromethyl mercaptan product formed is subsequently rapidly separated from other reactive products under conditions which also minimize these undesirable reactions such as Equation 6 which result in product losses.

It has ,also been found that the presence of excess carbon disulfide over the stoichiometric amount required in Equation 4 tends to increase the selectivity of the reaction in the direction of perchloromethyl mercaptan by the reaction of Equation 4 as compared to the undesired production of carbon tetrachloride. The preferred excess of carbon disulfide is in the range of convenience, the boiling points of the normally ll 20%-100%. The actual molar quantities preferi and is cooled to a temperature of -15 0.

entially employed are in the range of 1% mois to 2 mols of carbon disulde to each 3 mols of chlorine. This phenomenon oi increased selectivity is probably due to the depression of the chlorine partial pressure by the presence of excess carbon disulfide. This excess of CS2 represents a margin of safety, as an excess of only 16% chlorine over the indicated stoichiometrical amount is suflicient to convert all the perchloromethyl mercaptan to carbon tetrachloride if allowed to react.-

In order to remove S012 from the reaction zone, at low temperatures for the reasons discussed above, a vacuum distillation may be used. The process oi.' this invention preferably accomplishes the removal of the S012 at low temperatures in the presence of excess 0014 vapors accumulated in the process which serve as an inert atmosphere and prevent the beforementioned degradation reactions.

Auxiliary inert gas stripping agents may be employed in the distillation of the 0014 and more volatile materials from the perchloromethyl mercaptan. Thus 002, N2 and other gases boiling below about 100 C. may be used. Water is not desirable for use as it hydrolyzes the S012. The use of the indicated stripping agents increases equipment size needs, however, and also renders the condensation of the desired volatile products more difficult. The use of stripping agents may consequently be dispensed with.

The selectivity obtained by the process of this invention, i. e.. utilizing the indicated temperatures, excess carbon disulfide and rapid removal of reactive materials, results in selectivities of 90% as compared to 60% selectivities obtained by the prior art (Gilman and Blatt, "Organic Synthesis, Coll. vol. I, page 506).

This invention will be better understood by reference to the now diagram shown in the drawing.

In the system shown, fresh carbon disulilde enters the chilled reaction zone 3 through lines I and 2. Chlorine enters the reaction zone 3 through line 2. The mixture is agitated strongly The reaction mixture, after a period of 1 to 15 minutes, is withdrawn through line 4 to a distillation tower 5, which is maintained at atmospheric or subatmospheric pressures. Y

Warm C014 vapors which enter the tower 5 below the feed point through line I1 heat the predominantly liquid mixture to its boiling point and carbon tetrachloride and the reactant mixture of S012, CS2, and traces of chlorine, are rapidly taken overhead through line 6 to tower I3. Some C014 condenses in tower 5 and :flows down the tower as a, liquid with the perchloromethyl mercaptan. The liquid mixture leaves tower 5 through line I 9 and enters reboiler 20. The 0014 is vaporized and returned to tower 5 through line 22. The remaining liquid consisting predominantly of perchloromethyl mercaptan is withdrawn through line 2|.

'Operation of tower 5 in the manner indicated also prevents the development' of excessive tem'- peratures at localized areas which would result in product decomposition and degradation.

While the C014 vapor stream has been shown entering the tower; below the feed point through line I1, it may also enter at other points and still achieve the desired resul In distillation tower I3 the carbon disulnde is rapidly taken overhead through line 1, cooled and condensed in condenser 8, and passed through sure. "tute a reactive system. It

line 8 into drum I 0. A portion of the carbon disulde condensate containing dissolved traces of chlorine is recycled through line I2 to line 2 and reaction zone 3. The residual portion of the condensate in drum I0 is refluxed throughv line I I to tower I3.

The liquid mixture tetrachloride and S01: is withdrawn through line Il to distillation tower I5, which is maintained at atmospheric or slightly subatmospheric pres- The liquids in tower l5 no longer constiis desirable, however. to conduct this distillation rapidly to prevent S012 decomposition. The S012 is taken overhead through line I6. The major portion of the carbon tetrachloride may be withdrawn as a vapor from a lower portion of tower I5 through lIne I1 to distillation tower 5. The carbon tetrachloride vapors thus serve as the heating agent in tower l. Sutlicient liquid carbon tetrachloride to prevent buildup in the system is withdrawn through line I8.

The chlorine may enter reaction zone 3 through a plurality of points rather than at one point as described.

The reaction zone is maintained at approximately atmospheric pressure or higher. Since the chlorine is maintained largely in the liquid phase because of its solubility, there is no need for going to very high pressures.

The reaction mixture may be withdrawn from the reactionzone after the early period of reaction, i. e., 15 minutes, toa holding zone, cooling drum 24 through line 23. Most of the exothermic heat of reaction is evolved during this early period. Use of an auxiliary cooling drum permits of lesser refrigeration and agitation in this equipment while the temperature is maintained in the desired range, and permits the reaction to proceed further to completion. The mixture is then sent to the tower 5 through lines 25 and l.

The perchloromethyl mercaptan withdrawn through line 2 is relatively free from S1301: and may be used as is,- or further purified by means such as, for example, mild alkaline scrubbing. vacuum or ordinary distillation.

Catalysts known in the art for chlorination. suchas iodine, ferrie chloride, and aluminum chloride, are desirably utilized in the reaction and can be removed from the products if desired by standard procedures, such as by washing with an aqueous medium, vacuum or ordinary distillation, ltration, treating with `mild reducing agents such as thiosulfate, etc. The reactor strip- L Example I A reaction product mixture of the following Y proportion o1 starting materials. 1 mole of CS: to 3.1 moles of C12, catalyzed by iodine, was distilled .in the ordinary manner at atmospheric pressure. The chlorine iigure represents chlorine actually absorbed and taken up by the CS2. The products obtained were 40 vol. per cent S2012. 53 vol. per cent C014 and 7 vol. per cent SCI: with no perchloromethyl mercaptan. The latter had apparently all undesirably been converted to CCl4.

of predominantly carbon i Example II A series of runs were made in which the ratio of chlorine to CS2 was varied from 0.5 mole of C12/mole CS2 to 2.5 moles C12/mole' CS2. The latter ratio represents the maximum at which the excellent selectivities given above can be obtained. The following run was made with the chlorine concentration at the upper end of the desired level.

A reaction product mixture of the following proportion of starting materials, 1 mole of CS2 to 2.4 moles of C12, catalyzed by iodine, was distilled in the manner of this invention. The chlorine gure represents chlorine actually absorbed and taken up by the CS2. The products obtained were 48 vol. per cent perchloromethyl mercaptan (98% pure, only little SzClz), 7 vol.

per cent CCl4, 37 vol. per cent SClz and 8 vol.`

per cent CS2.

This illustrates the necessity of the rapid removal of the SClz from the reaction zone at lower temperatures than ordinary atmospheric distillation and the desirability of keeping the concentration of reactants within the preferred range.

Another advantage of the process of this invention resides in the recovery of the SClz which is a valuable by-product.

It is to be understood that the invention is not limited to the specic examples which have been oiered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A process for the continuous preparation of perchloromethyl mercaptan which comprises the steps of reacting carbon disulfide and chlorine in a reaction zone at a temperature in the range of 15 C., the carbon disulfide being present in an amount of 1% mole to 2 moles per 3 moles of chlorine; withdrawing the resulting predominantly liquid reaction mixture to a first distillation zone; quickly removing at subatmospheric pressure from said rst distillation zone a vaporous mixture of carbon tetrachloride, SClz, carbon disulfide, and traces of chlorine; rapidly separating the carbon disulde and chlorine from theV sate containing some dissolved chlorine; recycling a portion of said carbon disulde condensate to the reaction zone; reuxing a residual portion of the condensate to the second distillation zone; withdrawing a liquid bottoms mixture comprising predominantly carbon tetrachloride and SClz from the second distillation zone to a third distillation zone; rapidly distilling the SClz from the third distillation zone; withdrawing carbon tetrachloride as a bottoms liquid from the third distillation zone; withdrawing a carbon tetrachloride vapor stream from/ said bottoms liquid of the third distillation zone; recycling this carbon tetrachloride vapor stream to the rst distillation zone; and removing perchloromethyl mercaptan as bottoms from the rst distillation zone.

2. A process as in claim 1 in which the carbon tetrachloride vapor stream is returned to the rst l distillation zone at a point below the feed point.

3. A process as in claim 2 in which the withdrawn liquid bottoms from the distillation zone is reboiled to vaporize any carbon tetrachloride contained therein and the thus vaporized carbon tetrachloride is returned to the distillation zone.

ERNEST O. OHSOL. CARL S. CARLSON. BOYD E. HUDSON, JR.

REFERENCES CITED Organic Syntheses (Coll. vol. I) by Gilman and Blatt (2nd ed.) pages 506-509.

Schechter, JACS, vol. 63 (1941), pp. 1764-1765. Helfrich, JACS, vol. 43 (1921). pp. 590-592. 

1. A PROCESS FOR THE CONTINUOUS PREPARATION OF PERCHLOROMETHYL MERCAPTAN WHICH COMPRISES THE STEPS OF REACTING CARBON DISULFIDE AND CHLORIDE IN A REACTION ZONE AT A TEMPERATURE IN THE RANGE OF 0*-15* C., THE CARBON DISULFIDE BEING PRESENT IN AN AMOUNT OF 11/2 MOLE TO 2 MOLES PER 3 MOLES OF CHLORINE; WITHDRAWING THE RESULTING PREDOMINANTLY LIQUID REACTION MIXTURE TO A FIRST DISTILLATION ZONE; QUICKLY REMOVING AT SUBATMOSPHERIC PRESSURE FROM SAID FIRST DISTILLATION ZONE A VAPOROUS MIXTURE OF CARBON TETRACHLORIDE, SCI12, CARBON DISULFIDE, AND TRACES OF CHLORINE; RAPIDLY SEPARATING THE CARBON DISULFIDE AND CHLORINE FROM THE VAPOROUS MIXTURE TAKEN OFF FROM THE FIRST DISTILLATION ZONE IN A SECOND DISTILLATION ZONE; COOLING AND CONDENSING EFFLUENT VAPORS FROM THE SECOND DISTILLATION ZONE TO FORM A CARBON DISULFIDE CONDENSATE CONTAINING SOME DISSOLVED CHLORINE; RECYCLING A PORTION OF SAID CARBON DISULFIDE CONDENSATE TO THE REACTION ZONE; REFLUXING A RESIDUAL PORTION OF THE CONDENSATE TO THE SECOND DISTILLATION ZONE; WITHDRAWING A LIQUID BOTTOMS MIXTURE COMPRIS- 